Thin-Film Sensor Element With Segmented Resistance Structure
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Solution Overview
Problem
Existing thin-film resistance thermometers face challenges in achieving high accuracy due to production fluctuations, mechanical stresses from thermal expansion mismatches, and the influence of intermediate conductors and encapsulation materials, which affect the precision of temperature measurements, especially at low temperatures.
Innovation Solution
A thin-film sensor element with a resistance structure that branches into parallel sections within the resistive area, forming internal reference points, and using a four-wire circuit configuration to minimize the impact of intermediate conductors and thermal stresses, along with a substrate and cover layer thermal expansion coefficient matching the resistance structure to reduce mechanical stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a thin-film resistance thermometer uses a meandering resistance structure to achieve required length for measurable resistance, then the resistance value can be adjusted, but the structure becomes complex and is sensitive to mechanical stresses from thermal expansion mismatches
Solution Approach 1:
The resistance structure is divided into multiple straight segments connected by intermediate conductors, where each segment can be independently optimized. This segmentation allows the structure to achieve required resistance values without complex meandering patterns, reducing sensitivity to thermal expansion stresses while maintaining manufacturability.
Solution Approach 2:
Intermediate conductors are introduced as mediator elements connecting the resistance structure to external circuitry. These intermediaries isolate the resistance structure from mechanical stresses caused by thermal expansion mismatches, protecting the measurement function while simplifying the overall structure.
2Reliability
If intermediate conductors and encapsulation materials are used to protect and connect the resistance structure, then the sensor becomes functional, but thermal expansion mismatches create mechanical stresses that reduce measurement accuracy
Solution Approach 1:
The patent modifies the physical parameters of intermediate conductors and encapsulation materials, specifically their thermal expansion coefficients and mechanical properties, to better match the resistance structure. This parameter optimization reduces thermal stress while maintaining protective and connective functions.
Solution Approach 2:
The sensor employs composite material structures where intermediate conductors and encapsulation layers are specifically selected and combined to create a system with matched thermal expansion characteristics. This composite approach allows simultaneous achievement of structural integrity and measurement precision.
3Measurement precision
If a four-wire circuit configuration is used to eliminate the influence of connecting conductors, then resistance measurement precision improves, but the device complexity and number of connections increase
Solution Approach 1:
The patent combines the four-wire circuit configuration with the segmented resistance structure and intermediate conductors, merging multiple functions into a unified design. The intermediate conductors serve both as structural elements and as part of the measurement circuit, reducing overall complexity while maintaining high measurement precision.
4Ease of manufacture
If the resistance structure is designed at a temperature different from the nominal temperature with mathematical correction, then production becomes more flexible, but the design process becomes more demanding and accuracy is compromised
Solution Approach 1:
The patent applies preliminary thermal stress compensation during the manufacturing process by pre-adjusting the resistance structure or selecting materials with matched thermal properties. This preliminary action eliminates or reduces the need for complex mathematical corrections, maintaining both production flexibility and measurement accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances the accuracy of temperature measurements by isolating the resistance measurement from external influences, achieving high precision and reducing hysteresis effects, thereby meeting stringent accuracy standards like class 1/5 B or 1/10 B according to DIN EN 60751:2009-05.
Implementation Method 1
Materials referred to as PTC thermistors have proven to be particularly suitable for resistance thermometers, since the resistance of PTC thermistors increases linearly in the first order as the temperature rises
Implementation Method 2
using a substrate and cover layer thermal expansion coefficient matching the resistance structure to reduce mechanical stresses
Data Source
Figure 1a~1c
Figure 2~4d
AI summary
The invention relates to a thin-layer sensor element (1) for determining and/or monitoring temperature. To this end, a resistor structure (4) is provided that is arranged on a substrate (2) in a resistor area (3). The resistor structure (4) is structured such that a first section (5) of the resistor structure (4) branches into two paths (51, 52) at a first reference point (53), and that a second section (6) of the resistor structure branches into two further paths (61, 62) at a second reference point (63). In a contact area (7), the four paths are connected to four intermediate conductors (81, 82, 83, 84) in four contact pads (71, 72, 73, 74) that are insulated from one another. Therefore, the thin-layer sensor element (1) is a genuine four-conductor sensor element, the reference points (53, 63) of the four-conductor circuit being situated within the resistor area (3). The resistance thermometer (13) having the thin-layer sensor element (1) according to the invention is highly accurate.